1. Field of the Invention
The present invention relates to a camera system having a data communication function between a camera body and a photographing lens.
2. Description of Related Art
In a known single lens reflex camera having an automatic focusing device, data, such as, for example an open F-number peculiar to the photographing lens used for an automatic exposure function, or an automatic focus function is sent as electrical signals to a CPU provided in the camera body from the photographing lens.
To this end, the photographing lens used in the single lens reflex camera includes a lens ROM in which data peculiar to the photographing lens is stored. A plurality of electrical contacts are provided on the lens mount of a photographing lens and the body mount of a camera body to transmit and receive the data therebetween.
The CPU of the camera body performs the data communication with the lens ROM through the electrical contacts to read the data stored in the lens ROM. Necessary data is outputted from the lens ROM in accordance with address signals which are sent thereto from the CPU synchronously with clock pulses output from the camera body.
However, in a single lens reflex camera in which an AF (auto focus) motor and a PZ (power zoom) motor are provided in the photographing lens, if the control of the AF and PZ motors is effected by the CPU of the camera body, the CPU receives an over-load. In particular, the operation of a single lens reflex camera in which a variety of photographing lenses can be exchangeably mounted to the same camera body is quite slow, due to the fact that the CPU of the camera body must read different parameters depending on the photographing lenses from the lens ROM to perform predetermined arithmetic operation to thereby control the photographing lenses.
Various kinds of data for the different types of photographing lenses which can be attached to the camera body, such as judgment data which determines whether the photographing lens attached to the camera body is the type in which an auto focus control is possible, etc., are stored in the lens ROM. Therefore, a large part of the memory (capacity) of the lens ROM is used for that data, so that it is either necessary to erase data in order to rewrite new data or it is necessary to replace the existing ROM with a larger ROM, which is troublesome.